Liquid-phase non-thermal plasma-prepared N-doped TiO₂ for azo dye degradation with the catalyst separation system by ceramic membranes

This study strived to improve the photocatalytic activity by using liquid-phase non-thermal plasma (LPNTP) technology for preparing N-doping TiO₂ as well as to separate/recover the N-dope TiO₂ particles by using ceramic ultrafiltration membrane process. The yellow color N-doped TiO₂ photocatalysts, obtained through the LPNTP process, were characterized with UV–Vis spectroscopy, X-ray diffraction (XRD), and electron spectroscopy for chemical analysis (ESCA). The UV–Vis spectrum of N-doped TiO₂ showed that the absorption band was shifted to 439 nm and the band gap was reduced to 2.82 eV. The structure analysis of XRD spectra showed that the peak positions and the crystal structure remained unchanged as anatase after plasma-treating at 13.5 W for 40 min. The photocatalytic activity of N-doped TiO₂ was evaluated by azo dyes under visible light, and 63% of them was degraded after 16 hours in a continuous-flow photocatalytic system. For membrane separation/recover system, the recovery efficiency reached 99.5% after the ultrafiltration had been carried out for 90 min, and the result indicated that the photocatalyst was able to be separated/recovered completely.